High tension insulator



July 16, 1935. c. 1.. STROUP HIGH TENSION INSULATOR Filed May 26, 1933 Patented July 16, 1935 UNITED STATES PATENT OFFICE HIGH TENSION INSULATOR Application May 26, 1933, Serial No. 673,093

6 Claims.

This invention is an insulator of the high tensiontype.

In Letters Patent 1,851,671 issuedto Robert M.

Johnstonet al. on March 29, 1932, is illustrated and described a high tension insulator comprising-a dielectric body having an axially disposed chamber-constructed and arrangedto receive a suspension pin. Said'pinis anchored within the chamber by means of a suitable'metal, prefer- 10 ably one'which is capable of being applied while in a-molten condition, said metal possessing the necessary mechanical strength to firmly unite the dielectric bodyand the pin, in such manner as to resist all normal strainstending-to separatethem. As shown in the drawing ofthe patcut, the exposed surface of the alloy'is covered to a substantial depth by a waterproofing material. In practical operation, however, it has been found that there is a concentration of electrostatic-field at the-end surface of th metal closet tothe air, which condition has a tendency-to produce a concentration of dielectric stress, and also tends to reduce the puncture voltage'of the insulator.

One of the objects of the present invention is to provide an-insulator of the type above'described constructed and arranged to prevent the concentration of dielectric stress at the metal surface, and thereby very materially raise the 80 puncture voltage and uniformity of the insulator structure. A further object is to accomplish the desired results by providing a covering material for the'metal which has what may be termed 'a grading effect or the characteristic of variable conductivity from the metal to the air, reliancebeing placed upon the metal for mechanical strength, the covering material being utilized purely because of its effect upon the electrical functions.

The invention will behereinafter fully set forth and particularlypointed out in the claims.

In'the accompanyingdrawing, the figure is a side elevation partly in section illustratingan insulator constructed vin accordance with the invention.

Referring to. thedrawing, I designates .an insulator of ,suitabledielectric material, such as porcelain for instance, provided with a hub-like portion H of any desired contour. A flange or petticoat i2 is formed integrally with the hub- -like portion, and provided with depending annular ribs i3 to increase the leakageand flash over 1 I distances. The dielectric body thus far described may be of any desired conformation, the

design shown in the drawing having been selected for illustrative purposes only; and without insulator is provided with a central axially disposed chamber !4, open to the air at the lower end as illustrated in the drawing, the open end being slightly flared.

The hub-like portion I! is enclosed within a correspondingly shaped metal cap I5, preferably of pressed steel. This cap may be secured to the hub in any suitable or desired manner, but for purposes of illustration it is shown as connected to the dielectric material in the manner described in the above identified patent. For

instance, the cap !5 is shown as being of somewhat larger diameter than that of the hub H, so as to provide a substantial space between them, said space being filled by an asphaltum waterproofing material indicated at IS. The cap is also shown as slightly flared at its lower edge, as indicated at l6, and provided with an'inwardly extended annular flange i1. Interposed between the mouth portion of the cap and the adjacent portion of the dielectric body, and interlocking with theflange i1, is a metallic anchorage 18, preferably consisting of a metal capable of being applied while in a molten condition. The features thus far described are shown in the J ohnstonet al. patent above identified, and are not claimed in this application.

The central chamber M is illustrated as provided with a suitably roughened wall portion at the inner end thereof, preferably in the form of screw threads or corrugations 2%), and the suspen sion pin- 2! is provided with similar corrugations 22, in the form of a screw thread. The inner end of the pin 2! bears against a resilient washer 23, such as cork or the like interposed between said end and the inner end wall of the recess [4. Said pin is anchored to the interior of the chamber l4 by means of a metal thimble 24, preferably made of a metal capable of being applied while in a molten condition. This metal is preferably zinc or zinc alloy because it may be poured into the space between the pin 35 and the adjacent wall of the recess, and possesses the characteristicthat it will shrink slightly upon cooling. It will be noted that the metal fills the spaces between the corrugations and the screw threads 22, andprovides an absolutely firm and strong anchorage for the pin, possessing great mechanical strength.

The anchorage 24, while in position presents an annular ring-like outer or lower end surface which would normally be exposed to the atmosphere and if not properly covered is the cause of a very strong concentration of the electrostatic field at the exposed surface. Therefore, some material must be provided to cover this surface,

in such manner as to provide a gradingeiiect of electric conductivity, whichwill prevent concenv ,tration of said dielectric stress at the alloygsurintent to 'lirnitthe invention. The body of the face. The waterproof covering employed in the Johnston et al. patent, above identified will not perform this function. However, it has been Cal Cement is known to be relatively dry at the surface which is exposed to the air, but is somewhat damp at the portion next to-the metal.

dition produces a remarkable grading effect upon the electric conductivity from the metal to the air, which prevents he concentration of the dielectric stress at the alloy surface, and as an important result, it very materially raises the puncture voltage and uniformity of the insulator as a whole. It is of decided advantage in suspension insulators employing metallic alloy as the means of carrying the mechanical stresses. In practice .it is preferred to'interpose an asphaltum waterproofing compound between the longitudinal wall of the recess and the grading material 25, and also to cover the exposed outer end surface of said grading material in a similar manner. Said waterproofing material is indicated at 26.

. It is preferred to use neat Portland cement as the grading material, but other substances of graded conductivity may be employed, such as any hydraulic cement either neat, or admixed with sand, iron filings, or semi-conducting substances, such as carborundum dust. Among other cements may be mentioned litharge-glycerine, plaster of Paris, and lime. Any of these substances will function to grade the electro conductivity from a maximum at the outer end of the metal to a minimum at the outer end of the grading material, where the latter contacts with the air.

The advantages of the invention will be readily understood by those skilled in the art to which it belongs.

For instance, the value of an insulator is known to depend upon its ability to withstand puncture under the stresses of carrying the high Voltage current. By employing a suitable material for grading the conductivity from the metal to the air, a most important result is obtained, in that by preventing the concentration of l the dielectric stress at the metal surface, the puncturevoltage of the insulator, as well as the uniformity of its insulating functions, are very materially improved.

Having thus explained the nature of the invention and described an operative manner of constructing and using the same, although without attempting to set forth all of the forms in which it may be made, or all of the forms of its use, what is claimed is:-

l. An insulator of the character described comprising a dielectric body having an axially disposed central recess, a pin of less diameter than a the recess and having a portion extended longitudinally thereinto, a metallic anchorage filling the space between a portion of said pin and an adjacent portion of the longitudinal wall of said It has been demonstrated that this hygroscopic conrecess, and a body of material of variable electroconductivity filling the space between another portion of the pin and an adjacent portion of the longitudinal wall of the recess, and covering the outer surface of said metallic anchorage in such .manner as to prevent formation of a concentrated electrostatic field in the vicinity of said metallic nchor e.

3. An insulator of the character described comprising a dielectric body having a central axially disposed recess, the inner portion of the longitudinal wall of said recess being roughened, a suspension pin having a portion extended into said recess, said extended portion being roughened at a locality adjacent to the roughened portion of said recess, said pin being of less diameter than the recess, a metallic anchoring material filling the space between the pin and the wall of the recess and constructed and arranged to interlock with said roughened portions and firmly anchor the pin to the dielectric body, and a material of variable electric conductivity covering said metallic anchoring material and interposed between the same and the air, said material being constructed and arranged to prevent formation of a concentrated electrostatic field at the surface of the alloy.

4. An insulator of the character described comprising a dielectric body having a central recess, a pin having a portion extended into said recess, a metallic anchoring material interposed between said pin and the adjacent longitudinal wall of said recess, and constructed and arrangedto retain said pin in said recess, a covering interposed between the outer end of said metallic anchoring material and the air, said covering being of variable conductivity and constructed and arranged to prevent the formation of a concentrated electrostatic field at the surface of said metal, a waterproofing material interposed between said grading material and the adjacent longitudinal wall of said recess, and a similar waterproofing material covering the outer end of said grading material.

of the recess and constructed and arranged to firmly connect the pin with said dielectric body,

. and the body of cement interposed between the lower edge of said metallic anchoring means and the air, said cement being constructed and arranged to prevent concentration of electrostatic field at the surface of the alloy.

6. An insulator of the character described comprising a dielectric body having 'a central axially disposed recess, a pin having a portion extended into said recess longitudinally and of less diameter than the recess, a thimble-like metallic anchorage interposed between "said pin and the adjacent wall portion of said recess, said anchorage being constructed of a metal capable of being applied while in a molten state, said thimble having an annular outer edge portion, and a body of cement located in the lower portion of said recess and so positioned as to engage and cover said annular outer edge. of the metal anchorage, said cement being constructed and arranged to prevent concentration of electrostatic field at said annular edge. r

' CHARLES L. STROUP. 

